DESCRIPTION (provided by investigator): The ability of experimentalists to perturb biological systems has traditionally been limited to rigid pre- programmed protocols or more flexible, but reflex constrained, operator-controlled protocols. In contrast, "real-time control" allows the researcher to dynamically probe a biological system with parameter perturbations that are calculated functions of instantaneous system measurements, thereby providing the ability to address diverse unanswered questions that are not amenable to traditional approaches. Real-time control applications are abundant throughout biological research, including, for example, dynamic probing of ion-channel function, control of cardiac arrhythmia dynamics, and control of deep-brain stimulation patterns. Unfortunately, for a number of technical reasons, real-time control is not possible with standard computer operating systems and software. To circumvent these limitations, we have developed a fast and highly versatile real-time biological experimentation system known as Real-Time eXperiment Interface (RTXI), which is based on Real-Time Linux, is open source and free, and has been adopted by many prominent laboratories. Although RTXI is already being used successfully for a range of experiments, there remain important development avenues that would significantly expand its functionality and broaden its utility for the biological research community, and which therefore comprise the specific aims of this renewal proposal: 1. To periodically update RTXI's base code and plugins so that RTXI remains current. 2. To incorporate several new features that will facilitate the ongoing experiments of RTXI end users. 3. To broaden RTXI's real-time experiment application space to support two techniques for which real- time control is well-suited: optical mapping and two-photon imaging. 4. To broaden the experiment-design options, beyond the current options of direct source-code or script editing, by adding block-diagram and drag-and-drop visual-design tools. 5. To improve usability through the development of professional documentation and a user tutorial. By accomplishing these goals, this project will open new avenues of research and enable novel insights that are unavailable with traditional experimentation approaches. PUBLIC HEALTH RELEVANCE: (Using no more than two or three sentences, describe the relevance of this research to public health.) Traditional experimentation protocols are not always capable of fully probing the mechanisms of complex biological systems. We have developed a free, open-source software system, known as Real-Time eXperiment Interface (RTXI), that enables experimentalists to perform protocols that are adapted on-the-fly to maximize or optimize information acquisition during the course of an experiment. This project, which aims to expand the functionality of RTXI in significant ways, will further the abilities of biological scientists to use such protocols to learn important information about biological systems ranging from the heart to the brain.